Biochips enable parallel analysis of a very large number of molecules, essentially nucleic acids and proteins. The basic principle is recognition and pairing of two molecules that have affinities.
One of the collections of molecules is fixed in the form of minideposits or microdeposits on a solid support, fabric, glass slide, silicon chip, etc. The other molecule, which is labeled and generally in solution, is brought into contact with the samples deposited on the solid support. After an incubation period, the excess of labeled molecule is eliminated and the support is carefully washed. It is then necessary to detect and quantify the signal emitted by the molecules retained on the deposits. In certain cases, the retained molecule can be uncoupled from the deposits and a new molecule can be tested with the same solid support.
In order to process biochips, it is generally necessary to bring the deposits into contact with different reagents and then to wash them carefully. It is necessary to adjust the temperature of the reagents and the biochips. The most frequently employed tags are fluorescent, but other labeling techniques can be used.
The labeled molecule is a rare and/or expensive element. It is desirable to minimize the volume required. The other reagents, particularly the washing products, are not expensive and the reduction of the volumes used is much less important.